The purpose of this study was to investigate how situational interest of high school students was triggered during a field trip to an aquarium. Although the role of museums in stimulating interest among students has been acknowledged for some time, empirical evidence about how the specific variable of a museum setting might trigger situational interest is almost nonexistent. The present study was conducted as a case study to provide an inductive, explorative investigation of how situational interest emerged during the field trip. A situative approach to the study of interest was applied in the form of a combined analytical tool that captures both social and psychological aspects. Qualitative methods were used to generate data: observation, video recording, and interviews. The findings showed that the aquarium visit triggered a lot of situational interest among the students and led to positive emotions toward the topic. Five situational variables were found to trigger the students’ interest: social involvement, hands-on, surprise, novelty, and knowledge acquisition. The situational variables are largely under the control of the teacher and/or museum staff and should be considered when planning museum visits. This study suggests that teachers can find ways to foster students’ involvement in specific content areas and increase levels of academic motivation regardless of prior interest.